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ARM: by default don't set the Thumb bit on MachO relocated values.

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Its existence is largely historical, apparently we tried to make ARM object
files look maybe-almost-possibly runnable by putting our best guess at the
actual value into relocated locations. Of course, the real linker then comes
along and can completely change things.

But it should only be there for word-sized and movw/movt relocations. It can't
be encoded in branch relocations, and I've seen it mess up validity
calculations twice in the last couple of weeks so the default is clearly problematic.

llvm-svn: 279773
This commit is contained in:
Tim Northover 2016-08-25 20:41:30 +00:00
parent 0209a4ca21
commit 35c35dd4f1
3 changed files with 42 additions and 10 deletions
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21
lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
View File

@ -541,7 +541,7 @@ unsigned ARMAsmBackend::adjustFixupValue(const MCFixup &Fixup, uint64_t Value,
//
// Note that the halfwords are stored high first, low second; so we need
// to transpose the fixup value here to map properly.
if (Ctx && Value % 4 != 0) {
if (Ctx && Value % 4 != 0) {
Ctx->reportError(Fixup.getLoc(), "misaligned ARM call destination");
return 0;
}
@ -703,15 +703,16 @@ void ARMAsmBackend::processFixupValue(const MCAssembler &Asm,
bool &IsResolved) {
const MCSymbolRefExpr *A = Target.getSymA();
const MCSymbol *Sym = A ? &A->getSymbol() : nullptr;
// Some fixups to thumb function symbols need the low bit (thumb bit)
// twiddled.
if ((unsigned)Fixup.getKind() != ARM::fixup_arm_ldst_pcrel_12 &&
(unsigned)Fixup.getKind() != ARM::fixup_t2_ldst_pcrel_12 &&
(unsigned)Fixup.getKind() != ARM::fixup_arm_adr_pcrel_12 &&
(unsigned)Fixup.getKind() != ARM::fixup_thumb_adr_pcrel_10 &&
(unsigned)Fixup.getKind() != ARM::fixup_t2_adr_pcrel_12 &&
(unsigned)Fixup.getKind() != ARM::fixup_arm_thumb_cp &&
(unsigned)Fixup.getKind() != ARM::fixup_arm_thumb_cb) {
// MachO (the only user of "Value") tries to make .o files that look vaguely
// pre-linked, so for MOVW/MOVT and .word relocations they put the Thumb bit
// into the addend if possible. Other relocation types don't want this bit
// though (branches couldn't encode it if it *was* present, and no other
// relocations exist) and it can interfere with checking valid expressions.
if ((unsigned)Fixup.getKind() == FK_Data_4 ||
(unsigned)Fixup.getKind() == ARM::fixup_arm_movw_lo16 ||
(unsigned)Fixup.getKind() == ARM::fixup_arm_movt_hi16 ||
(unsigned)Fixup.getKind() == ARM::fixup_t2_movw_lo16 ||
(unsigned)Fixup.getKind() == ARM::fixup_t2_movt_hi16) {
if (Sym) {
if (Asm.isThumbFunc(Sym))
Value |= 1;

2
test/MC/ARM/aligned-blx.s
View File

@ -27,8 +27,10 @@ _test:
blx _aligned @ PC=0 (mod 4)
movs r0, r0
blx _aligned @ PC=2 (mod 4)
blx _f1
@ CHECK: blx _elsewhere
@ CHECK: ff f7 fa ef blx _aligned
@ CHECK: ff f7 f8 ef blx _aligned
@ CHECK: ff f7 f6 ef blx _aligned
@ CHECK: ff f7 f2 ef blx _f1

29
test/MC/ARM/macho-word-reloc-thumb.s Normal file
View File

@ -0,0 +1,29 @@
@ RUN: llvm-mc -triple thumbv7-apple-ios %s -filetype=obj -o %t
@ RUN: llvm-objdump -macho -d %t -triple thumbv7-apple-ios | FileCheck %s
@ ARM relocatable object files try to look like they're pre-linked, so the
@ offsets in the instructions are a best-guess. I suspect the "-3" should b
@ CHECK: movw r1, :lower16:((_bar-8)-3)
@ [...]
@ CHECK: .long {{[0-9]*[13579]}}
.thumb
.thumb_func _foo
_foo:
movw r1, :lower16:(_bar-(LPC2_0+4))
movt r1, :upper16:(_bar-(LPC2_0+4))
LPC2_0:
add r1, pc
ldr r0, Lconstpool
bx lr
Lconstpool:
.data_region
.word _bar
.end_data_region
.thumb_func _bar
_bar:
bx lr
.subsections_via_symbols